In case it wasn’t clear from the title, this week’s episode of "Doctor Who" clearly underlines the importance of the number three. There’s The Doctor, Amy, and Rory; there’s cubes everywhere; and the most important power of three: the three act structure. It’s with that last one where writer Chris Chibnall doesn’t quite stick the landing, delivering a fun first two acts, and then bungling the episode in the last. It wasn’t without worth, but it’s the third act that does this episode in.

I want to emphasize: it starts off really promisingly, with tiny black cubes that do nothing “invading” the entire world. For Whovians, this should set off all sorts of time travel/alternate universe headache type questions: is this the first alien invasion that’s happened in the timeline? What about Torchwood? Or are we somewhere or when else? It doesn’t matter that much, as the cubes get summarily ignored, and used more as paperweights than anything else.

The Doctor, meanwhile, is going nuts. Amy and Rory have decided to try their hand at not jaunting all over the universe, and are starting to enjoy hanging out with friends. Even with the cube invasion, they’re not interested in leaving… While The Doctor, who is on hand to study the cubes, can’t sit still for five minutes.

Luckily, Brian – Rory’s Dad – can sit still for five minutes… And in fact, watches his cube night and day for nearly an entire year. That is, of course, when he’s not side-eyeing the Doctor, and asking uncomfortable questions about what happens to his Companions when he’s done with them.

And there’s your first act! Weird, unexplained cubes, Matt Smith playing Wii Tennis, and everybody generally being weird and British. You know the other shoe is going to drop, but the mystery is so goofy and strange, it’s fun to watch.

Then, in Act Two, the cubes start moving. Amy gets her blood tested, Rory gets his reflexes tested, and the Doctor gets shot at. Naturally. All around the world, the cubes are waking up, and doing different things – from causing emotional reactions, to playing the Mexican Hat Dance on a loop. Enter UNIT, the elite weird hunting organization from past episodes of Who, and the new Brigadier Stewart… Kate Stewart, played by Jemma Redgrave.

If you guessed she’s the daughter of classic Who character Brigadier Lethbridge-Stewart, well, give yourself fish sticks and custard.

Back to UNIT, who find not only are the cubes acting up, but they’ve been testing humanity… And then they start counting down. Are they bombs? Are they something worse? Nope, they’re just going after a metaphor by stopping everyone in close range’s hearts, including 50% of The Doctor’s.

All good so far… The heart attack twist keeps up the weirdness, though it downsizes the mystery of the cubes considerably. Also, we’re introduced to a weird girl with blue eyes holding a cube, and two orderlies in a hospital stealing human bodies, with cube shaped holes in their mouths.

Act Three! Tracing a signal, they discover the cubes were actually created by one of those alien races that were folktales for the Timelords, basically alien exterminators. They’re getting rid of humanity before they can spread throughout the universe like a virus. Except the aliens aren’t even there, they’re holograms. And The Doctor reverses their machine with his sonic screwdriver. Then he and the Pond/Williams escape the ship just as it explodes.

Brian, in a twist, tells the Ponds they should keep traveling with the Doctor, Brigadier Stewart says, “The Power of Three!” and everybody jumps in the air, high fives, and freezes.

Just kidding about the last part, but I really can’t imagine that would have made the mess of a third act any worse. There’s a number of huge problems with it, not least of which that the mystery of the cubes gets steadily less interesting as it goes. Here’s some others!

- The orderlies are stealing people to take to their ship. Why, exactly?

- Also: they get completely blown up at the end. No-one is concerned about this?

- Cubes are sent all over the world, but only heart attack about a third of the population? That’s the plan? If I had exterminators who guaranteed to get rid of 33% of my cockroaches, I think I might fire them.

- I’m sorry, but it’s just poor writing to introduce a villain no one has heard of, with no real relation to the main characters five minutes before the end.

- Brian also totally reverses, saying Amy and Rory should travel with the Doctor… Something that barely follows on everything that’s come before.

That last point is the biggest stickler, and I guess we’ll have a better idea of the narrative arc of this shortened season next week, but here’s how it breaks down now:

Episode 1: The Ponds need to be brought back together, they miss traveling. The Doctor is getting a bit weird without them.

Episode 2: The Doctor realizes they have each other, don’t need him. He basically kills a dude because he’s spiraling into darkness.

Episode 3: The Ponds stop the Doctor from killing another dude, he stops spiraling into darkness! They start to feel like maybe they want to just go home.

Episode 4: The Ponds decide to leave the TARDIS and have a life… But really they don’t want to and everybody is happy again!

Episode 5: Bye bye, Ponds.

Again, it’ll be clearer once next week is in the books, but that doesn’t look so much like an arc, as a zig-zag to me. I also realize every episode is supposed to be like a stand-alone movie… But it’s not. The first episode, yes. The second episode, maybe. The past two episodes? Nope. And even barring that, this is a TV show, not a series of movies, or even TV movies. They’re going to be judged as a unit no matter what.

Next week is the third and final act of the Ponds' story on the TARDIS. Here’s hoping we can really, truly feel the Power of Three.